Environment Science & Technology

The hidden dangers of climate change: Huge reserves of mercury found in arctic permafrost

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One of the most pressing but often over-looked concerns with increasing global temperature and climate change are the dangers gradually revealing themselves to scientists from unexpected, previously unconsidered sources. An example of this is the hospitalisation of 72 Nordic herders in Northern Russia as a result of an anthrax outbreak caused by unusually high temperatures thawing ice containing long-since frozen animal carcasses. Scientists have now discovered that permafrosts may hide another potentially deadly threat to ecosystems, massive reserves of mercury hidden in permafrost in the Northern Hemisphere. The research reveals scientists examining permafrost in Alaska that has been building since the last major ice-age, have found mercury content in the permafrost is approximately double the concentrations currently found in ground soil, the atmosphere and the world’s oceans combined making this the largest reservoir of mercury on the planet by a large margin.

The paper published in the February edition of the Geophysical Letters explains in its introduction how mercury builds up in permafrost over time “Over thousands of years, sedimentation buried mercury (Hg) bound to organic material and froze it into the permafrost. Permafrost is soil at or below 0°C for at least two consecutive years. The active layer is the surface soil layer on top of the permafrost that thaws in summer and refreezes in winter. Hg deposits onto the soil surface from the atmosphere, where it bonds with organic matter in the active layer. Microbial decay then consumes the organic matter, releasing the Hg. At the same time, sedimentation slowly increases soil depth such that organic matter at the bottom of the active layer becomes frozen into permafrost. The organic matter consists almost entirely of plant roots, and, once frozen, microbial decay effectively ceases, locking the Hg into the permafrost. However, permafrost has begun to thaw under a changing climate. Once the permafrost and associated organic matter thaws, microbial decay will resume and release Hg to the environment, potentially impacting the Arctic Hg balance, aquatic resources, and human health.”

Maps of mercury concentrations (micrograms of mercury per square meter) in Northern hemisphere permafrost zones for four soil layers: 0-30 centimeters, 0-100 centimeters, 0-300 centimeters, and permafrost. The permafrost map represents the mercury bound to frozen organic matter below the Active Layer Depth (ALD) and above 300 cm depth.
Credit: Schuster et al./GRL/AGU.

Paul Schuster, a hydrologist at the U.S. Geological Survey in Boulder, Colorado and lead author of the new study explains the significance of the study’s results “We’ve quantified a pool of mercury that had not been done previously, and the results have profound implications for better understanding the global mercury cycle. There would be no environmental problem if everything remained frozen, but we know the Earth is getting warmer,” Schuster said. “Although measurement of the rate of permafrost thaw was not part of this study, the thawing permafrost provides a potential for mercury to be released—that’s just physics.”

Study authors Kim Wickland and Paul Schuster drilling a permafrost core at the Bonanza Creek Experimental Forest (BCEF) southwest of Fairbanks, Alaska.
Credit: Bob Eganhouse

Schuster and colleagues drilled 13 permafrost soil cores of variable lengths in Alaska, finding that more than 15 million gallons, of mercury, is frozen in northern permafrost soil. That is roughly 10 times the amount of all human-caused mercury emissions over the last 30 years, based on emissions estimates from 2016. The study also found all frozen and unfrozen soil in northern permafrost regions contains a combined 1,656 gigagrams of mercury, which is what makes this the largest known reservoir of mercury on the planet.

The dangers represented in these findings

As warmer air temperatures due to climate change begin to thaw the permafrost releasing groundwater, this could lead to excessive levels of mercury leaching from soil to waterways around the world. This would almost inevitably lead to the build-up of mercury in aquatic and terrestrial food chains when microorganisms take up mercury and transform it into the highly toxic form, methylmercury.

sketch of the cycle of the bioaccumulation of methylmercury

Methylmercury is different than another compound of mercury, ethylmercury found as a preservative in some vaccines and is known to have severe health effects. These range from toxic effects on the nervous, digestive and immune systems, as well as significant risks to children in utero. The World Health Organisation (WHO) ranks it as one of the top ten deadliest compounds to human health.

Alaskan communities rely heavily on sustenance methods and will be first hit by methylmercury build up in local food chains.

Whilst the findings from this study primarily represent a major danger to rural Alaskan communities who rely mainly on sustenance lifestyles, mercury released in the atmosphere and into waterways, can travel large distances, so the effect is not likely to remain localised for long.

Steve Sebestyen, a research hydrologist at the USDA Forest Service in Grand Rapids, Minnesota, who was not involved with the new research made commented on the paper “There’s a significant social and human health aspect to this study. The consequences of this mercury being released into the environment are potentially huge because mercury has health effects on organisms and can travel up the food chain, adversely affecting native and other communities.”

Future implications of this research. Climate change’s stark warning

Clearly one of the next steps in this research is to establish just how much of this stored mercury would be released into local ecosystems if global temperatures are to continue to rise and what the effect of that event would be. Whilst this study alone gives both environmental scientists and policy makers much to consider, there is a much more profound aspect lurking in the details of this study. Before this research was conducted, no one had actually considered measuring the levels of mercury in permafrost. This was a potential danger that no one was actually aware of, much like risks posed by long frozen bacteria as described in my opening paragraph. The threat of this mercury reservoir could have quite easily gone undiscovered until it was too late.

Nature is trying to tell us, in none to subtle ways, that the dangers of climate change are far more insidious than we have predicted. That majorly altering the planet’s ecosystems will have hidden, lethal effects on not just our species but many other forms of life on the planet.

We ignore this message to our own detriment.